This case study recounts the attempts of two school districts to improve decision making on the adoption of a new elementary social studies curriculum by using formal evaluation methodology. The study's main objective was to develop a series of criterion referenced (mastery level) tests from a list of social studies objectives to determine whether these objectives were taught more effectively by the new curriculum. Other objectives included: developing a firm data base for decision making; involving teachers and principals in a field test to assess curriculum objectives; and projecting a plan for an inservice program. Drawing on the technical resources of the University of Illinois, the districts conducted a field evaluation of the new curriculum. Two groups of students were administered the tests; the experimental group received instruction in the new curriculum, while the control group was exposed to the more traditional curriculum. A total of 1086 students in 48 classrooms participated. Findings indicated the experimental group consistently made higher gains in achievement than the control group. It was also concluded that although criterion referenced evaluation provided important information, traditional test analysis measures proved to be more useful for making decisions on adoption and for planning teacher inservice programs. (Author/JK)